During the conceptualizing phase of creating the "Legends of Saviors" titles, it was imperative to create the planets not just when the players would visit them, but the entire history of each one, as well.
During the 3rd, last, and most present Phase of Jagg, we can see that the planet has changed completely and irrevocably - being flash-frozen in a sheet of thick ice that seems to never melt. Before this horrible event happened, however, many of the Khestlings built a giant home for themselves in the center of their planet, locking off the outside world with a giant, mechanical gate underwater (and now, under the ice).
LoS Concept Art | Jagg, Part 3 - Present Phase Time-Lapse